Work in LMB has led the way towards the ambitious goal where stem cells can be used to replace tissue damaged by neurodegenerative diseases that cause the loss of neurons or glial cells. We have previously demonstrated that stem cells derived from the fetal brain can generate neurons that secrete the neurotransmitter dopamine but these cells can provide unlimited numbers of these neurons. In the last year we have continued to develop embryonic stem (ES) cells as a source of dopamine neurons. These are the type of neuron lacking in Parkinson?s patients and these neurons have not previously been obtained in such large numbers. Parkinson's disease (PD) is a widespread neurological condition caused by the loss of neurons in the midbrain that synthesize the transmitter dopamine. Clinical experience suggests that cells derived from the fetal midbrain can modify the course of the disease. The limited supply of this tissue may be overcome by new stem cell technologies. Precursors from the fetal brain are not an adequate source of these neurons because their ability to generate dopamine neurons is not stable. In contrast, embryonic stem (ES) cells proliferate extensively and can generate dopamine-synthesizing neurons. If ES cells are to become the basis for cell therapies, it is critical to develop systematic methods to enrich for the cell of interest and demonstrate that these cells show functions that will assist in understanding and treating the disease. Here we show that a highly enriched population of midbrain neural stem cells can be derived from ES cells. The dopamine neurons generated by these stem cells show electrophysiological and behavioral properties expected of neurons from the midbrain. These results encourage further development of the potential of ES cells in cell replacement therapy for Parkinson's disease.